Cup type grinding wheel

ABSTRACT

Cup type grinding wheel to be attached to a rotary tool includes a plastic base plate made of a glass fiber-reinforced plastic, a metal annular plate with pieces of grindstone on a fixing surface of the metal annular plate, and fasteners for integrating the plastic base plate with the metal annular plate. Heads of fasteners are positioned at the same level as the fixing surface or at a lower level than the fixing surface toward the plastic base plate.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the foreign priority benefit under Title 35, United State Code, 119 (a)-(d) of Japanese Patent Application Nos. 2012-132377 and 2012-170565, respectively filed on Jun. 11 or Jul. 31, 2012 in the Japan Patent Office, each disclosure of which is herein incorporated by reference in each entirety.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a cup type grinding wheel which is attached to a rotary tool such as a sander and for grinding a hard product like a concrete or ceramics-related thing, cutting it or tearing off coating of it and so on.

2. Description of Background Art

There are a flat type grinding wheel and a cup type grinding wheel in the prior art of a grinding wheel to be attached to a rotary tool. The former is a grinding wheel at a periphery of abase plate like a circular plate of which tips like cutting blades or cutter blades are fixed, the latter is one at a periphery of a base plate with a central projecting portion of which tips are fixed. They are disclosed, for example, in the patent document 1 (JP, patent No.3634794) or the patent document 2 (JP, patent No.4009278). In the cup type grinding wheel, a fastener like nut to fix a drive mechanism of the rotary tool to the cup type grinding wheel thereby is positioned inside the central projecting portion of the base plate. So a whole of a bottom surface of the grinding wheel can approach a surface of a work piece to be machined or approach an adjacent surface of that of the work piece so that tips of the grinding wheel abuts on the work piece. Therefore, machining a corner portion of the work piece or grinding a wide surface of it can be efficiently done.

However, a base plate to fix tips of the cup type grinding wheel in the patent documents 1 or 2 is heavy, because it is made of a metal such as aluminum or steel. Therefore, there is a problem that a working load is great when a user operates a rotary tool equipped with the cup type grinding wheel attached thereto with one hand. And, there is also a problem that power consumption in the rotary tool with the cup type grinding wheel is large, because the weight of the cup type grinding wheel is heavy.

Furthermore, as a metal base plate is poor in elasticity, the metal base plate cannot fully absorb vibrations or shocks generated while working such as grinding, cutting or tearing off a coating (each of these is named working hereinafter) is underway so that tips or pieces of grindstone on the grinding wheel do not keep uniform pressure on a work piece. Therefore, the work piece is damaged or portions like wrinkles which are not machined in the work piece are generated because tips or pieces of grindstone do not abut on the portions. Thus there is a problem that a poorly smoothed surface is made on a work piece.

BRIEF SUMMARY OF THE INVENTION

Therefore, the present invention is conceived in view of the foregoing problems. It is an object of the present invention to provide a cup type grinding wheel a weight of which is light and which can attain a machined surface with a good smoothness of a work piece.

According to the present invention to solve the foregoing problems, there is provided a cup type grinding wheel having a recessed portion formed by a projection of a central part of a plastic base plate like a circular plate to dispose a plurality of pieces of grindstone, and the cup type grinding wheel enabling to be attached to a drive mechanism of a rotary tool through an attachment hole formed at a central plane of the recessed portion, comprising:

the plastic base plate made of a glass fiber-reinforced plastic in which a nylon resin is reinforced by glass fibers, and including

a mounting surface like a flat plate to dispose the plurality of pieces of grindstone,

a slant surface of the recessed portion connected with the mounting surface and having a predetermined angle of slope, and

the central plane of the recessed portion connected with the slant surface and forming the attachment hole therein;

a metal annular plate of a metal plate formed in an annular shape including

an abutting surface abutting on the mounting surface, and

a fixing surface fixing the plurality of pieces of grindstone on an opposite side to the abutting surface;

the plurality of pieces of grindstone fixed at a periphery of the fixing surface at a predetermined interval; and

a plurality of fasteners passing through the mounting surface and the fixing surface at positions except positions of the plurality of pieces of grindstone so that the plastic base plate and the metal annular plate are integrated with each other,

wherein the plurality of fasteners are disposed at a predetermined interval in a circumferential direction of the mounting surface and the fixing surface and integrate the plastic base plate with the metal annular plate so that a head of each of the plurality of fasteners is positioned at the same level as the fixing surface of the metal annular plate or at a lower level than the fixing surface toward the plastic base plate.

By the foregoing cup type grinding wheel, the weight of the cup type grinding wheel can be lightened in comparison with the prior one having the metal base plate because the plastic base plate is used in the present cup type grinding wheel. As the plastic base plate can be appropriately deformed when the cup type grinding wheel is used, vibrations of the cup type grinding wheel can be absorbed and shocks of that can be also softened. As a result, the cup type grinding wheel keeps uniform pressure on a work piece. Especially, the pieces of grindstone of the cup type grinding wheel can abut on a concavo-convex surface in correspondence to the up-down change of the concavo-convex surface of the work piece without jumping even if a face of the work piece has the concavo-convex surface. Furthermore, as the plastic base plate absorbs vibrations of the cup type grinding wheel, harsh sounds caused by the vibrations dies away. Still more, as the plastic base plate is made of a glass fiber-reinforced plastic, a heat resistance and strength of the plastic base plate improve so that a damage of the plastic base plate can be prevented during a working operation.

A head of a fastener does not contact with a work piece and the head is not ground down during a working operation thanks to integrating the plastic base plate and the metal annular plate with each other so that a head of each of fasteners is positioned at the same level as the fixing surface of the metal annular plate or at a lower level than the fixing surface toward the plastic base plate. In consequence of this, each fastener is prevented from coming off and the cup type grinding wheel is prevented from being damaged.

It is preferable that the cup type grinding wheel according to the present invention further comprises an elastic sheet like an annular plate made of an elastic material between the mounting surface and the abutting surface.

By this embodiment having the elastic sheet, the elastic sheet absorbs vibrations and shocks when the cup type grinding wheel is used. Therefore, the vibrations of the cup type grinding wheel are more absorbed and the shocks of the same are also further reduced so that the cup type grinding wheel abutting on a work piece keeps uniform pressure on the work piece. And thanks to the elastic sheet, harsh sounds caused by the vibrations further dies away, and a fastener is prevented from making inroads into the plastic base plate due to the vibrations in use of the cup type grinding wheel, so the plastic base plate can be certainly prevented from being damaged.

It is preferable that the cup type grinding wheel according to the present invention further comprises a cylindrical sleeve disposed to let both through holes of the plastic base plate and the elastic sheet communicate with each other which through holes each of the plurality of fasteners passes through, and each of the plurality of fasteners passes through the metal annular plate and the sleeve to integrate the plastic base plate, the elastic sheet and the metal annular plate with each other.

By this embodiment having the sleeve, the elastic sheet is not compressed excessively in use of the cup type grinding wheel so that an elastic action thereof is not prevented. Therefore, the action to absorb the vibrations or the shocks generated in use of the same improves. Thereby, the cup type grinding wheel abutting on a work piece keeps uniform pressure on the work piece. And harsh sounds caused by the vibrations further dies away, and a fastener is prevented from making inroads into the plastic base plate due to the vibrations in use of the cup type grinding wheel, so the plastic base plate can be certainly prevented from being damaged.

It is preferable that each fastener of the cup type grinding wheel according to the present invention is a rivet.

By this embodiment having a rivet as a fastener, the rivet is not loosened due to the vibrations or the shocks in use of the cup type grinding wheel in comparison with a bolt as a fastener. Therefore, an integration of the plastic base plate and the metal annular plate becomes strong, so a damage of the cup type grinding wheel can be certainly prevented.

It is preferable that each fastener of the cup type grinding wheel according to the present invention is a rivet, and a body of the rivet has a small-diameter part passing through the metal annular plate and a large-diameter part passing through the plastic base plate and the elastic sheet so that a shoulder is formed between the small-diameter part and the large-diameter part.

By this embodiment having a rivet with a shoulder as a fastener, the elastic sheet is not compressed excessively in use of the cup type grinding wheel so that an elastic action thereof is not prevented. Therefore, the action to absorb the vibrations or the shocks generated in use of the same improves. Thereby, the cup type grinding wheel abutting on a work piece keeps uniform pressure on the work piece. And harsh sounds caused by the vibrations further dies away, and a fastener is prevented from making inroads into the plastic base plate due to the vibrations in use of the cup type grinding wheel, so the plastic base plate can be certainly prevented from being damaged.

It is preferable that each piece of grindstone of the cup type grinding wheel according to the present invention is fixed on the fixing surface by firing to integrate them.

By this embodiment having pieces of grindstone fixed on the fixing surface by firing to integrate them, each piece of grindstone is prevented from falling off from the fixing surface due to the vibrations or the shocks in use of the cup type grinding wheel.

A rotary tool equipped with the cup type grinding wheel according to the present invention can be operated by one hand because the cup type grinding wheel is light. So fatigue burdens on a worker decreases, and power consumption in the rotary tool with the cup type grinding wheel is also reduced. And a damage of a work piece can be prevented and the work piece can also be prevented from generating portions like wrinkles which are not machined, because pieces of grindstone on the cup type grinding wheel according to the present invention keep uniform pressure on a work piece. Therefore, a machined surface superior in smoothness can be obtained and fatigue burdens on a worker also decrease. Furthermore, the cup type grinding wheel according to the present invention can prevent harsh sounds due to vibrations, so a noise to the surrounding area and hearing burdens on a worker decrease. Still more, the present cup type grinding wheel prevents the plastic base plate or the cup type grinding wheel itself from being damaged so that the safety for a worker improves. Further, the present cup type grinding wheel does not need to be repaired or to be exchanged, so machining cost is lowered and workability improves.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a plan view showing an embodiment of a cup type grinding wheel according to the present invention;

FIG. 2 is a partial sectional view taken along the line A-A of FIG.1;

FIG. 3 is an exploded perspective view of an essential part showing an integrating structure of a plastic base plate and a metallic annular plate;

FIG. 4 is an enlarged partial sectional view showing an integrating structure of a plastic base plate and a metallic annular plate of FIG. 2;

FIG. 5 is a plan view showing another embodiment of a cup type grinding wheel according to the present invention;

FIG. 6 is an enlarged partial sectional view of an essential part showing another embodiment of a cup type grinding wheel according to the present invention;

FIG. 7 is a plan view showing another embodiment of a cup type grinding wheel according to the present invention;

FIG. 8 is a partial sectional view taken along the line B-B of FIG. 7;

FIG. 9 is an enlarged partial sectional view of an essential part showing another embodiment of a cup type grinding wheel according to the present invention; and

FIG. 10 is a plan view showing another embodiment of a cup type grinding wheel according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A first embodiment of a cup type grinding wheel (the grinding wheel, hereinafter) according to the present invention will be explained in detail with reference to the attached drawings.

The grinding wheel 1A is attached to a drive mechanism 52 of a rotary tool 51 such as a sander as shown in FIGS. 1 to 4, and is for grinding a hard product (a work piece, hereinafter) like concrete or ceramics-related product, cutting it or tearing off coating of it and so on. The grinding, the cutting or the tearing off is named “working” hereinafter. The grinding wheel 1A includes a plastic base plate 2, a metal annular plate 8, apiece of grindstone 11 and a fastener 13. Hereinafter, each structure will be explained.

The plastic base plate 2 is a circular plate member and has a recessed portion 3 formed by a projection of a central portion thereof. An attachment hole 7 is bored through a central plane 6 of the recessed portion 3. Through the attachment hole 7, the grinding wheel is attached to the drive mechanism 52 of a rotary tool 51. Furthermore, the plastic base plate 2 has a mounting surface 4 like a flat face to dispose pieces of grindstone 11 which will be mentioned also later on a peripheral portion thereof, a slant surface 5 of the recessed portion 3 formed in a central portion thereof with a predetermined slant angle 0 relative to the mounting surface 4 and continuously connected with the mounting surface 4, and the central plane 6 of the recessed portion 3 forming the attachment hole 7 therein and continuously connected with the slant surface 5. Moreover, a plurality of through holes 4 a are formed along on a circle on the mounting surface 4 at a predetermined interval d so that each of them corresponds to a position of each through hole 9 a of the metal annular plate 8 to communicate with each other. Each fastener 13 passes through each through hole 4 a and each of the through holes 9 a to couple the plastic base plate 2 with the metal annular plate 8 which will be mentioned later. A tube-like portion (not shown) which is projected in a bent form like an L shape may be formed on the central plane 6 of the recessed portion 3 of the plastic base plate 2. And a screw member, for example, a female screw member inserted into an inner side of the tube-like portion by molding may replace the attachment hole 7. That is, the drive mechanism 52 of the rotary tool 51 can be attached to the plastic base plate 2 through the screw member.

The plastic base plate 2 can be properly curved thanks to the recessed portion 3 in a central portion of the plastic base plate when the grinding wheel 1A is abutted on a work piece during a working operation. Because of the plastic base plate 2 being curved, vibrations generated in the working, especially Z direction's vibrations are absorbed, and the plastic base plate 2 being curved serves so that shocks are moderated. Therefore, a noise is reduced. The Z direction is one along a rotational axis of the plastic base plate. The Z direction's vibration of the plastic base plate according to the present invention is reduced by about 40 percent in comparison with a prior metal base plate. The noise is also reduced by about 3 to 4 dB. These are confirmed by the inventors. The form of the recessed portion 3 of the plastic plate 2 is not limited as far as the foresaid operation is realized. For example, in the case that the grinding wheel 1A is used for tearing off a coating layer on a concrete product, it is preferable that an inner diameter D2 of the recessed portion 3 is 40 to 90 percent of an outer diameter D1 of the plastic base plate 2. And it is preferable that a height H of the recessed portion 3 is 10 to 30 percent of the inner diameter D2. Furthermore, it is preferable that a slant angle θ of the slant surface 5 of the recessed portion 3 is 20 to 90 degrees. The slant angle θ may be changed in accordance with positions in a direction of back to forth, or left to right on the plastic base plate 2. These are not shown. In case machining force or machining performance of the grinding wheel 1A is lowered due to the deformation of the plastic base plate 2, it is desired that the machining force or machining performance of the grinding wheel 1A is improved by changing a shape, a size, a degree of concentration, or the like of an abrasive grain or a combination of bond or the like constructing a piece of grindstone 11 to be mentioned later.

It is preferable that a width D3 of the mounting surface 4 of the plastic base plate 2 is 5 to 30 percent of the outer diameter D1 of the plastic base plate 2 so that it enables to form a through hole 4 a for a fastener 13 to pass through. And an embodiment is designated in FIGS. 2 to 4 which embodiment has an elastic sheet 15 to be mentioned later between the plastic base plate 2 and the metal annular plate 8. In the case that the elastic sheet 15 is not superimposed, the mounting surface 4 has a surface shape corresponding to that of an abutting surface 9 of the metal annular plate 8 to be mentioned later in order that the mounting surface 4 tightly abuts on the abutting surface 9 of the metal annular plate 8 without gap. Further, an inner diameter D4 designating the margin of the central plane 6 and an outer diameter D5 of the attachment hole 7 formed in the central plane 6 are adequately determined in accordance with a shape and a size of the drive mechanism 52 of the rotary tool 51 to which the grinding wheel 1A is attached.

The plastic base plate 2 is made of a glass fiber-reinforced plastic in which a nylon resin is reinforced by glass fibers. It is preferable that a glass fiber-reinforced plastic in which Nylon 66 is reinforced by glass fibers is used for the plastic base plate 2, an example of which is TECAMID 66 GF 30, a brand name of Ensinger Co., Ltd. The weight of the plastic base plate 2 is reduced, and a heat resistance or strength thereof improves thanks to the plastic base plate 2 made of the glass fiber-reinforced plastic. Especially in the case that the plastic base plate 2 is made of the glass fiber-reinforced plastic in which Nylon 66 is reinforced by glass fibers, a heat deformation temperature of the plastic base plate 2 is around 250° C. So the plastic base plate 2 has a sufficient heat resistance or strength endurable for grinding a concrete product, that is, tearing off a coating layer on a concrete product. It is preferable that the glass fiber-reinforced plastic has glass fibers of 15 to 30 mass percent in whole mass including nylon resin in order to reduce a weight of the plastic base plate 2 and improve a heat resistance and strength thereof. In a case that the quantity of glass fibers is under 15 mass percent, the heat resistance and strength of the plastic base plate 2 tend to lower. And in a case that the quantity of glass fibers is over 30 mass percent, the strength of the plastic base plate 2 tends to lower. In addition, a thickness T of the plastic base plate 2 is adequately determined in accordance with a material of a work piece. In the case that the grinding wheel 1A is used for tearing off a coating of a concrete product, it is preferable that the thickness T is 2.0 to 5.0 mm to keep the strength of the plastic base plate 2 and avoid damage of the plastic base plate 2 considering a deformation of the plastic base plate 2 during a working.

The metal annular plate 8 is a plate member made of a metal such as aluminum or steel. And it is an annular plate member including an abutting surface 9 to abut on the mounting surface 4 and a fixing surface 10 to fix pieces of grindstone 11 thereon on the opposite side of the abutting surface 9. The metal annular plate 8 is preferably made of steel, more preferably, carbon tool steel like SK5. Forming a recessed portion 8 a to be mentioned later and fixing the pieces of grindstone 11 on the fixing surface 10 by firing to integrate them can be simultaneously done by making the metal annular plate 8 out of carbon tool steel. The metal annular plate 8 made of carbon tool steel can be easily deformed to form the recessed portion 8 a because the firing temperature in the present invention is 880° C. over A1 transformation temperature 723° C. An outer diameter of the metallic annular plate 8 is substantially equal to the outer diameter D1 of the plastic base plate 2, and an inner diameter thereof is substantially equal to the inner diameter D2 of the recessed portion 3. In this embodiment, the metal annular plate 8 is disposed on the outer side of an inner annular portion including an inner peripheral surface 2 b of the plastic base plate 2 formed to support the metal annular plate 8 at the inner edge thereof.

A plurality of through holes 9 a are formed in the metal annular plate 8 at a predetermined interval d along on a circle on the abutting surface 9 or the fixing surface 10 each of which holes passes through the abutting surface 9 and the fixing surface 10 and communicates with the through hole 4 a of the plastic base plate 2 so that the metal annular plate 8 and the plastic base plate 2 are integrated with each other by fasteners 13 therethrough. It is preferable that the predetermined interval d may be 1/16 to ⅙ of the outer diameter of the metal annular plate 8. In the case that the predetermined interval d is under 1/16 of the outer diameter, the number of the through holes 9 a is so many that the fracture strength of the metal annular plate 8 tends to decrease and a crack is easily created on the metal annular plate 8 during a working operation. Further, in the case that the predetermined interval d is over ⅙ of the outer diameter, the number of the through holes 9 a is so few that the strength of the integration of the plastic base plate 2 and the metal annular plate 8 tends to decrease and the grinding wheel 1A tends to be damaged. Still more, it is preferable that the through holes 9 a are formed at positions not close to an outer circumference edge 8B of the metal annular plate 8 but biased towards the center side thereof, that is, biased toward an inner circumference edge 8A. The strength of the metal annular plate 8 improves by forming the through holes 9 a at such positions so that cracks due to a cyclic fatigue during a working operation are prevented from generating therein.

A piece of grindstone 11 has diamond abrasive grains, abrasive grains of cubic crystal boron nitride (CBN), or the like which are hardened by adhesion, electrodeposition, sintering or the like. A plurality of pieces of grindstone 11 are fixed to a peripheral portion of the fixing surface 10 by a known prior method. And it is preferable that the pieces of grindstone 11 are integrated with the fixing surface 10 by firing in order to prevent each piece of grindstone 11 from dropping off from the fixing surface 10 when a work piece is machined by the grinding wheel 1A. Each piece of grindstone 11 integrated by firing is prevented from dropping off from the fixing surface 10 even when it is caught in a projection like a pin of the work piece. So it is superior in safety, cost, a process or work. Each piece of grindstone 11 may be formed of a metal bond of an alloy mainly containing copper, tin, iron, cobalt, nickel, or the like to improve a machining force or machining performance thereof.

It is preferable that at least one of a front end surface 11 a and a rear end surface 11 b of a piece of grindstone 11 which front end surface 11 a is on the front side of the piece of grindstone 11 in a rotational direction of the grinding wheel 1A is formed by a curved surface. Further, it is preferable that at least one of an outer side surface 11 c and an inner side surface 11 d of a piece of grindstone 11 which outer side surface 11 c is on the outer side of the fixing surface 10 is curved projecting toward the outside of the fixing surface 10. A machining accuracy for a work piece by the grinding wheel 1A improves because a piece of grindstone 11 has such an end surface formed by a curved surface or a curved side surface. Still more, it is preferable that the side surface 11 c of each of some pieces of grindstone 11 projects outside an outer peripheral surface 2 a of the plastic base plate 2. Thereby the plastic base plate 2 hardly hits a work piece and is protected. So the grinding wheel 1A enables to machine a side surface or a peripheral surface of a work piece.

It is preferable that apiece of grindstone 11 is fixed in a state that the longitudinal direction thereof is along a circular direction or a radial direction of the fixing surface 10. It is further preferable that both of a piece of grindstone 11 fixed along the circular direction and a piece of grindstone 11 fixed along the radial direction are disposed on the same plastic base plate 2. A machining accuracy for a work piece by the grinding wheel 1A improves because the pieces of grindstone 11 are fixed in such a state.

A fastener 13 is to couple the plastic base plate 2 with the metal annular plate 8, and is a rivet, a bolt or the like. The fastener 13 passes through the through hole 4 a of the mounting surface 4 of the plastic base plate 2 and a through hole 9 a of the metal annular plate 8 which through holes 4 a and 9 a are positioned at positions except positions at which the pieces of grindstone 11 are fixed. A rivet is preferable for a fastener 13 because it provides a great integration force and it is hard to loose during a working operation. An adhesive may be filled into the through holes 4 a and 9 a to prevent a fastener 13 from loosing due to vibrations or shocks during a working operation or due to an expansion or shrinkage caused by a difference in temperature between a summer and a winter.

A plurality of fasteners are disposed at a predetermined interval d along on a circle on the mounting surface 4 or the fixing surface 10. The fasteners 13 couples the plastic base plate 2 with the metal annular plate 8 so that a head of each of the fasteners 13 on the side of the metal annular plate 8 is positioned at the same level as the fixing surface 10 or at the lower level by a predetermined depth t, for example, 0.5 to 2.0 mm from the fixing surface 10 toward the plastic base plate 2. In the case that the metal annular plate 8 is not thicker enough than the head 14 of the fastener 13 as shown, for example, in FIG. 4, or is thinner than that, a recessed portion 8 a depressed toward the plastic base plate 2 is formed in the metal annular plate 8. That is, the metal annular plate 8 projects toward the plastic base plate 2 at the recessed portion 8 a. The through hole 9 a has an opening thereof in the recessed portion 8 a. Each fastener 13 passes through each through hole 9 a to couple the plastic base plate 2 with the metal annular plate 8 so that the head 14 of each of the fasteners 13 is positioned within each recessed portion 8 a. In the case that the metal annular plate 8 is thicker enough than the head 14 of the fastener 13 as shown in FIG. 6 or 8, the form of the recessed portion 8 a as shown in FIG. 4 is not adopted in which form the abutting surface 9 of a part of the metal annular plate 8 is projected toward the plastic base plate 2 to form the recessed portion 8 a. That is, a recessed portion 8 a (9 a in FIG. 8) is formed on the side of the fixing surface 10 and the abutting surface 9 keeps flat. Each fastener 13 passes through each through hole 9 a to couple the plastic base plate 2 with the metal annular plate 8, and the head 14 of each of the fasteners 13 is positioned within each recessed portion 8 a or 9 a.

It is preferable that the grinding wheel 1A according to the present invention further comprises an elastic sheet 15 in addition to the foregoing structure. The elastic sheet 15 is made of an elastic material such as soft synthetic rubber or synthetic resin, and is an annular sheet formed in about the same size as the metal annular plate 8. Through holes 15 a are formed in the elastic sheet 15 each of which communicates with the through holes 4 a and 9 a and through each of which a fastener 13 passes. The elastic sheet 15 intervenes between the mounting surface 4 of the plastic base plate 2 and the abutting surface 9 of the metal annular plate 8 so that it serves to furthermore absorb vibrations and soften shocks during a working operation. Still more, the elastic sheet 15 prevents each fastener 13 from making inroads into the elastic base plate 2 due to the vibrations or shocks during a working operation.

It is preferable that the grinding wheel 1A according to the present invention comprises fasteners 13A and fasteners 13B to be mentioned in the following. Each fastener 13A is disposed at a position near each of some pieces of grindstone 11 at a predetermined interval dA in a first circumferential direction as shown in FIG. 5. The interval dA is, for example, ⅛ to ⅓ of the outer diameter of the metal annular plate 8. Each fastener 13B is disposed at a position near the inner circumference edge 8A of the metal annular plate 8 at a predetermined interval dB in a second circumferential direction as shown in FIG. 5. The circle of an arrangement of the fasteners 13A corresponding to the first circumferential direction and the circle of an arrangement of the fasteners 13B corresponding to the second circumferential direction are concentric. The interval dB is, for example, 1/16 to ⅙ of the outer diameter of the metal annular plate 8. Furthermore, it is preferable that a fastener 13A near a piece of grindstone 11 and a fastener 13B near the inner circumference edge 8A are disposed one by one in turn along a circumferential direction, that is, in an undulating arrangement along the circumferential direction. Thereby, the plastic base plate 2, the elastic sheet 15 and the metal annular plate 8 are integrated more strongly in a closely-attached state with each other. In this case, through holes 4 a of the plastic base plate 2, through holes 15 a of the elastic sheet 15, through holes 9 a and recessed portions 8 a of the metal annular plate 8 to pass the fasteners 13A and 13B therethrough are also disposed in the undulating arrangement (not shown) along the circumferential direction of the plastic base plate 2, the elastic sheet 15 or the metal annular plate 8.

It is preferable that the grinding wheel 1A including the elastic sheet 15 according to the present invention further comprises sleeves 16 as shown in FIG. 6. Each sleeve 16 is a cylindrical tube disposed in a through hole 4 a of the plastic base plate 2 and the through hole 15 a of the elastic sheet 15 to let the through hole 4 a communicate with the through hole 15 a which hole 4 a and hole 15 a are formed to pass a fastener 13 therethrough. Each fastener 13 passes through the metal annular plate 8 and each sleeve 16, thereby the plastic base plate 2, the elastic sheet 15 and the metal annular plate 8 are integrated with each other.

Since the grinding wheel 1A is equipped with sleeves 16 as shown in FIG. 6, the elastic sheet 15 is prevented from being excessively compressed in the thickness direction thereof during a working operation so that the elastic sheet 15 is kept in a stable elasticity. Therefore, the elastic sheet 15 fully absorbs vibrations and softens shocks during a working operation. Furthermore, a fastener 13 is also prevented from making inroads into the plastic base plate 2 due to vibrations during a working operation. Accordingly, a material and a thickness of the sleeve 16 is not limited in particular as long as the elastic sheet 15 can absorb vibrations and/or shocks and contribute to a weight reduction of the grinding wheel 1A. For example, it is preferable that the sleeve 16 is made of a hard material such as SUS (stainless steel) or iron, and it is preferable that a thickness thereof is 1 to 3 mm.

The sleeve 16 is formed and disposed to let the through hole 4 a of the plastic base plate 2 communicate with the through hole 15 a of the elastic sheet 15 in FIG. 6. However, it may be formed and disposed to let the through hole 9 a of the metallic annular plate 8, the through hole 4 a of the plastic base plate 2 and the through hole 15 a of the elastic sheet 15 communicate with each other. This embodiment is not shown. And though the embodiment shown in FIG. 6 is an example using a rivet for a fastener 13, a bolt and nut may be used for a fastener 13.

In the grinding wheel 1A including the elastic sheet 15 according to the present invention, the elastic sheet 15 maybe prevented from being excessively compressed by using a rivet 17 shown in FIG. 9 to be mentioned later instead of the sleeve 16 mentioned above.

An operation of the grinding wheel 1A will be explained in the following.

The grinding wheel 1A is attached to the drive mechanism 52 of the rotary tool 51 through the attachment hole 7 of the plastic base plate 2 to fix them with a nut or the like as shown in FIG. 2 when the grinding wheel 1A is used to machine a work piece. The grinding wheel 1A fixed in such a manner is rotated to abut the pieces of grindstone 11 fixed on the metal annular plate 8 upon the work piece. The metal annular plate 8 fixing the pieces of grindstone 11 thereon in the grinding wheel 1A is integrated with the plastic base plate 2 superior in flexibility, curving performance and strength by fasteners 13. Therefore, the plastic base plate 2 absorbs or reduces vibrations or shocks which act on the pieces of grindstone 11 thanks to an adequate deformation of the plastic base plate 2 when a machining is done with the grinding wheel 1A. A head 14 of each fastener 13 does not contact with a work piece during a working operation because the head 14 of each of the fasteners 13 is positioned at the same level as the fixing surface 10 of the metal annular plate 8 or at the lower level from the fixing surface 10 toward the plastic base plate 2. Therefore, a work piece is prevented from being damaged or from generating wrinkles without being machined so that a machined surface superior in smoothness can be obtained. In the case that the grinding wheel 1A includes the elastic sheet 15 between the plastic base plate 2 and the metal annular plate 8, the elastic sheet 15 still more absorbs or reduces vibrations or shocks which act on the pieces of grindstone 11 thanks to an elasticity of the elastic sheet 15.

A second embodiment of the grinding wheel will be explained with reference to the attached drawings.

A grinding wheel 1B is attached to the drive mechanism 52 of the rotary tool 51 as shown in FIGS. 7 and 8, and is for grinding a hard product such as concrete or ceramics-related product, cutting it or tearing off its coating layer and so on. The grinding wheel 1B includes the plastic base plate 2, a metal annular plate 8, pieces of grindstone 12 and fasteners 13. And it is preferable that the grinding wheel 1B further comprises the elastic sheet 15.

Hereinafter, each structure will be explained. However, the plastic base plate 2 and the fastener 13 are not further explained because they are the same as those of the grinding wheel 1A (refer to FIGS. 1 and 2) in the aforementioned first embodiment.

A plurality of grooves 8 b to fix a piece of grindstone 12 in each of them are formed on a fixing surface 10 of the metal annular plate 8 of the grinding wheel 1B at a predetermined interval in a direction along the peripheral area of the metal annular plate 8. The metal annular plate 8 of the grinding wheel 1B differs from that of the grinding wheel 1A in this point. The piece of grindstone 12 differs from that of the grinding wheel 1A in the points that the piece of grindstone 12 is fixed in the groove 8 b but not on the planar section of the fixing surface 10, and that the piece of grindstone 12 is fixed with an inclination of a predetermined angle against a work piece (not shown).

A contact area on which the piece of grindstone 12 and a work piece contact with each other becomes small during a working operation in the case that the aforesaid grinding wheel 1B is used because the piece of grindstone 12 is fixed in the groove 8 b with the aforesaid inclination against a work piece. As a result, vibrations or shocks which act on the pieces of grindstone 12 are reduced so that a smoothness of a surface of a machined work piece further improves.

It is preferable that a rivet 17 is used for a fastener in the grinding wheel 1B according to the present invention and a shoulder 20 c is formed on a body 20 thereof as shown in FIG. 9 in the case that an elastic sheet 15 is provided. The rivet 17 includes a head 18 formed on the side of the metal annular plate 8, another head 19 formed on the side of the plastic base plate 2, and a body 20 between the heads 18 and 19. The body 20 has a small-diameter part 20 a which passes through a through hole 9 a of the metal annular plate 8 and a large-diameter part 20 b which passes through a through hole 4 a of the plastic base plate 2 and a through hole 15 a of the elastic sheet 15. The shoulder 20 c is formed between the small-diameter part 20 a and the large-diameter part 20 b.

A gap between an inner peripheral surface 15A of the elastic sheet 15 and an inner annular portion having an inner peripheral surface 2 b of the plastic base plate 2 may be formed, and/or a gap between an outer peripheral surface 15B of the elastic sheet 15 and an outer annular portion having an outer peripheral surface 2 a of the plastic base plate 2 maybe formed. These gaps are not shown. An expansion and contraction of the elastic sheet 15 can be smoothly achieved thanks to the gaps when the elastic sheet 15 is compressed in the thickness direction thereof. Therefore, it is hard for the elastic sheet 15 to be damaged. And the through hole 15 a may be formed as a hole having an opening that opens up to the peripheral surface of the elastic sheet 15, that is, some cutout portions (not shown) are formed on the outer peripheral surface 15B of the elastic sheet 15.

The elastic sheet 15 is not excessively compressed in the thickness direction by using the rivet 17 with the shoulder 20 c in the grinding wheel 1B shown in FIG. 9 when the grinding wheel 1B is used so that an elastic action thereof is not prevented. Therefore, the elastic sheet 15 serves efficiently to absorb vibrations and reduce shocks during a working operation. Furthermore, the rivet 17 is prevented from making inroads into the plastic base plate 2 due to vibrations during a working operation. Therefore, it is preferable that the ratio of outer diameters of the large-diameter part 20 b to the small-diameter part 20 a forming the shoulder 20 c is 1.3 to 3.0. However, the aforesaid ratio is not limited to that range as long as the elastic sheet 15 can serve to absorb vibrations and/or shocks and contribute to a weight reduction.

Further, in the case that the elastic sheet 15 is used in the grinding wheel 1B, the aforementioned sleeve 16 shown in FIG. 6 may be used instead of the rivet 17 with the shoulder 20 c so that the elastic sheet 15 can be prevented from being excessively compressed (not shown).

It is preferable that the metal annular plate 8 has projecting parts 21 at an inner circumference edge 8A thereof in the grinding wheel 1B as shown in FIG. 10 each of which parts projects towards a rotational center thereof. And a through hole 9 a to pass the fastener 13 (refer to FIG. 8) therethrough is formed on the same radial line as a symmetric line of the corresponding projecting part 21 to have an opening on the fixing surface 10.

A distance between the inner circumference edge 8A and the through hole 9 a of the metal annular plate 8 is held long thanks to the projecting parts 21 of the metal annular plate 8 in the grinding wheel 1B shown in FIG. 10. So even if a crack occurs at the inner circumference edge 8A due to vibrations or shocks during a working operation, it is prevented from propagating up to the through hole 9 a. Therefore, the metal annular plate 8 can be prevented from being damaged and the strength thereof improves. Consequently, the grinding wheel 1B is prevented from being damaged and safety for a worker improves.

It is preferable that a width of the metal annular plate 8 defined in the radial direction between the inner circumference edge 8A and the outer circumference edge 8B is held constant along the circumference of the metal annular plate 8, as long as a distance between the inner circumference edge 8A and the through hole 9 a is long enough, for improving the strength of the metal annular plate 8. However, though the strength of the metallic annular plate 8 improves in such a case, the weight thereof gets heavy so that a weight saving thereof becomes hard. On the contrary, each region having no projecting part 21 has a recessed contour that the inner circumference edge 8A is curved toward the outer circumference edge 8B, in the metallic annular plate 8 of the grinding wheel 1B shown in FIG. 10. So the metal annular plate 8 becomes light by the weight of the recessed areas so that the weight of the grinding wheel 1B can be reduced.

It is preferable that each of a width wA, a width wB and a width wC is over 1.0 mm to improve the strength of the annular plate 8 as mentioned above. The width wA is that between the through whole 9 a and the inner circumference edge 8A in the region having the projecting part 21. The width wB is that between the through whole 9 a and the outer circumference edge 8B. And the width wC is that between the groove 8 b to fix a piece of grindstone 12 therein and the inner circumference edge 8A in the recessed region having no projecting part 21 as shown in FIG. 10. It is more preferable that each of widths wA, wB and wC is over 2.0 mm. In the case that the width wA, wB or wC is under 1.0 mm, the strength of the metal annular plate 8 is not enough so that a crack tends to generate in the metal annular plate 8 during a working operation. Furthermore, it is preferable that the upper limit of the width wA, wB or wC is properly determined so that the weight of the metal annular plate 8 does not get too heavy.

The operation of the grinding wheel 1B will be explained in the following.

As shown in FIG. 8, the drive mechanism 52 of the rotary tool 51 is attached to the plastic base plate 2 to fix each other with a nut or the like when the grinding wheel 1B is used for machining a work piece. And the grinding wheel 1B is rotated, then the pieces of grindstone 12 fixed on the metal annular plate 8 are abut on the work piece. The plastic base plate 2 of the grinding wheel 1B is adequately deformed like that of the grinding wheel 1A (refer to FIG. 2) during a working operation so that vibrations or shocks which act on the pieces of grindstone 12 are absorbed or softened by the plastic base plate 2. Furthermore, the fasteners 13 do not contact with a work piece. In the consequence, a machined surface superior in smoothness can be obtained. And in the case that the grinding wheel 1B further comprises the elastic sheet 15, vibrations or shocks which act on the pieces of grindstone 12 are further absorbed or softened by the elastic sheet 15.

EXAMPLE

The example of the grinding wheel according to the present invention will be explained in the following.

The grinding wheel as shown in FIGS. 1 and 2 is made by using the following members.

(Plastic Base Plate)

A base plate made of a glass fiber-reinforced plastic (The brand name is TECAMID 66 GF 30) made by Ensinger Co., Ltd. whose outer diameter D1 is 123 mm, thickness is 3.5 mm, inner diameter D2 of the recessed portion 3 is 60 mm, height H of the recessed portion 3 is 13 mm, and the slant angle θ of the recessed portion 3 is 73 degrees is used.

(Metal Annular Plate)

A metal annular plate made of SK5 (carbon tool steel) whose width is 30.5 mm and thickness is 1.0 mm is used.

(Fastener)

A rivet made of stainless steel having a diameter of 4.0 mm is used.

(Piece of Grindstone)

A piece of grindstone made of diamond abrasive grains whose size is 6 mm×20 mm×4.5 mm is used. Each piece of grindstone is fixed to the peripheral portion of the metal annular plate by firing.

(Elastic Sheet)

A rubber annular plate whose width is 30.5 mm and thickness is 1.0 mm is used.

COMPARATIVE EXAMPLE

The same members as the above example are used except that a steel base plate is used instead of the plastic base plate, and a grinding wheel as shown in FIGS. 1 and 2 is made.

Each mass of the grinding wheels of the example and the comparative that is measured. The results are shown in Table 1. Each grinding wheel of the example and the comparative that is attached to the sander (PDA-100H) made by Hitachi Koki Co., Ltd. A surface of a coated steel plate that a steel plate is coated with epoxy resin twice by a brush is ground by using the sander with each grinding wheel, respectively. The coating film of the coated steel plate is removed by grinding with use of the sander so that the steel plate which is the foundation for the coating film is exposed. A surface roughness of the exposed steel plate is measured by a surface roughness tester (The type is Surf Test-4) made by Mitutoyo Corporation to be the index for a ground state. The results are shown in Table 1.

TABLE 1 Example Comparative example Mass (g) 145 254 R_(z) (μm) 7.9 17.1 . . . Measurement Point 1 (Maximum 6.8 16.2 . . . Measurement Point 2 Height 9.7 27.8 . . . Measurement Point 3 Roughness) 8.1 20.4 . . . Average R_(z) designates Maximum Height Roughness in JIS B 0601:2001.

As shown in Table 1, the weight reduction of the grinding wheel of the example is achieved in comparison with the comparative example. And the surface roughness thereof is smaller than the comparative example so that a superior machined surface is obtained.

Tests for shocks of the grinding wheel of the example are conducted under the following conditions while it is rotating. After ten times of tests, any fatigue destruction part is not observed in the grinding wheel of the example.

(Used Sander)

PDA-100H made by Hitachi Koki Co., Ltd. with the rotating speed of 12000 rounds/min

(Work Piece)

A commercial concrete board having the size of 30 cm×30 cm×3 cm (thickness)

(Machining Conditions)

A load for one piece of grindstone is 4 kgf in the shear direction.

A cut depth is 3 mm.

A cut length per 1 cut is 30 cm.

DESCRIPTION OF REFERENCE NUMERALS

-   1A,1B Cup type grinding wheel -   2 Plastic base plate -   3 Recessed portion -   4 Mounting surface -   4 a Through hole -   5 Slant surface -   6 Central plane -   7 Attachment hole -   8 Metal annular plate -   9 Abutting surface -   9 a Through hole -   10 Fixing surface -   11, 12 Piece of grindstone -   13, 13A, 13B Fastener -   14 Head -   15 Elastic sheet -   15 a Through hole -   16 Sleeve -   17 Rivet -   20 Body -   20 a Small-diameter part -   20 b Large-diameter part -   20 c Shoulder -   21 Projecting part -   51 Rotary tool -   52 Drive mechanism -   d, dA, dB Predetermined interval -   θ Predetermined slant angle 

What is claimed is:
 1. A cup type grinding wheel having a recessed portion formed by a projection of a central part of a plastic base plate like a circular plate to dispose a plurality of pieces of grindstone, and the cup type grinding wheel enabling to be attached to a drive mechanism of a rotary tool through an attachment hole formed in a central plane of the recessed portion, comprising: the plastic base plate made of a glass fiber-reinforced plastic in which a nylon resin is reinforced by glass fibers, and including amounting surface like a flat plate to dispose the plurality of pieces of grindstone, a slant surface of the recessed portion connected with the mounting surface and having a predetermined angle of slope, and the central plane of the recessed portion connected with the slant surface and forming the attachment hole therein; a metal annular plate of a metal plate formed in an annular shape including an abutting surface abutting on the mounting surface, and a fixing surface fixing the plurality of pieces of grindstone on an opposite side to the abutting surface; the plurality of pieces of grindstone fixed at a periphery of the fixing surface at a predetermined interval; and a plurality of fasteners passing through the mounting surface and the fixing surface at positions except positions of the plurality of pieces of grindstone so that the plastic base plate and the metal annular plate are integrated with each other, wherein the plurality of fasteners are disposed at a predetermined interval in a circumferential direction of the mounting surface and the fixing surface and integrate the plastic base plate with the metal annular plate so that a head of each of the plurality of fasteners is positioned at the same level as the fixing surface of the metal annular plate or at a lower level than the fixing surface toward the plastic base plate.
 2. A cup type grinding wheel as claimed in claim 1, further comprising an elastic sheet like an annular plate made of an elastic material between the mounting surface and the abutting surface.
 3. A cup type grinding wheel as claimed in claim 2, further comprising a cylindrical sleeve disposed to let both through holes of the plastic base plate and the elastic sheet communicate with each other which through holes each of the plurality of fasteners passes through, each of the plurality of fasteners passing through the metal annular plate and the sleeve to integrate the plastic base plate, the elastic sheet and the metal annular plate with each other.
 4. A cup type grinding wheel as claimed in claim 1, wherein each of the plurality of fasteners is a rivet.
 5. A cup type grinding wheel as claimed in claim 2, wherein each of the plurality of fasteners is a rivet.
 6. A cup type grinding wheel as claimed in claim 3, wherein each of the plurality of fasteners is a rivet.
 7. A cup type grinding wheel as claimed in claim 2, wherein each of the plurality of fasteners is a rivet, a body of the rivet having a small-diameter part passing through the metal annular plate and a large-diameter part passing through the plastic base plate and the elastic sheet so that a shoulder is formed between the small-diameter part and the large-diameter part.
 8. A cup type grinding wheel as claimed in claim 1, wherein each of the plurality of pieces of grindstone is fixed on the fixing surface by firing to integrate them.
 9. A cup type grinding wheel as claimed in claim 2, wherein each of the plurality of pieces of grindstone is fixed on the fixing surface by firing to integrate them.
 10. A cup type grinding wheel as claimed in claim 3, wherein each of the plurality of pieces of grindstone is fixed on the fixing surface by firing to integrate them.
 11. A cup type grinding wheel as claimed in claim 4, wherein each of the plurality of pieces of grindstone is fixed on the fixing surface by firing to integrate them.
 12. A cup type grinding wheel as claimed in claim 5, wherein each of the plurality of pieces of grindstone is fixed on the fixing surface by firing to integrate them.
 13. A cup type grinding wheel as claimed in claim 6, wherein each of the plurality of pieces of grindstone is fixed on the fixing surface by firing to integrate them.
 14. A cup type grinding wheel as claimed in claim 7, wherein each of the plurality of pieces of grindstone is fixed on the fixing surface by firing to integrate them. 